CS1 week 5 flashcards (MARIE, CPU, Memory...)
What is the main role of cpu
driving force of fetch, decode, execute instructions (cycle)
What are the 2 principle parts of the cpu
. The datapath
.The control unit
What does the datapath consist of
It consists of the ALU and registers which are connected to each other and to memory by data bus
What are registers
specialised forms of memory that has specific data stored inside it
Why are registers fast?
They are close in proximity to cpu
What does the control unit do
send signals to activate various components
to perform sequenced operations
.ensure instructions are fetched, decoded and executed in correct sequence
How is computer memory ordered
A linear array of addressable storage cells
What is a word
A storage cell of memory of fixed size
what does word addressable mean
cpu identifies specific storage cells (words) to read and write data to and from memory
what does it mean by byte addressable
cpu identifies data by bytes -smaller parts (usually half) of a word- eg if a word is 16 bits processor may identify particular 8 bits of memory rather than the word
How many memory locations is 4M X 16 Ram chips
4 x 2^20 16 bit memory locations
. M - 2^20
. 16 part of 4Mx 16 tells you no of bits
What are the 2 ways io devices can be connected 2 cpu through interfaces
. Memory mapped
.Instruction mapped
What does it mean by memory mapped
There is a reserved section of memory for input and output devices through which CPU interacts
What does it mean by instruction mapped
CPU has specific instructions for controlling i/o devices
what is a bus
An array of wires that simultaneously transmit a single bit along each line
What does an address bus/ line do
sends a memory address along the bus from the cpu to the RAM to specify the location in memory where data should be fetched or written to
.uni directional
What does the data bus do?
. conveys bits from one device to another
sends data to and from memory
control bus/ lines
determines the direction of data flow and when each device can access the bus
What does a clock do
synchronises activities of its various components
What is the cpu time equation
T = seconds / program X no of cycle / instruction X seconds/ cycle
What do interrupts do
.Alter the normal flow of execution of a program when an event of higher priority occurs
. There are procedures that directs the cpu on actions to take when an interrupt occurs to handle event
What is an example of an interrupt event
i/ o requests
operational errors (dividing by 0)
invalid instructions
What does Accumulator AC register do
16 bit register that hold data cpu will process
what does the MAR do
12 bit register the hold memory address of data referenced
what does MBR do
16 bits - hold data that has just been read from memory or is about to be written to memory
program counter
12 bit- holds the address of the next instruction to be executed
Instruction register
16 bit- holds instruction immediately before its execution
Input register (IN)
8 bit - holds data read from input device
output register
8 bit- holds data to be written to output device
How are registers connected
all of registers connected to each other and memory via a common data bus
what does the ISA (intruction set architecture)
specifies formate of instructions and operations the machine can perform
. is an interface between software and hardware
